In synchronous motors, especially of the type used on aircraft, a damper winding is used on a main machine rotor for improving generator transient performances. As the synchronous motor has no starting torque, some form of auxiliary power unit (APU) is used to supply power to drive an alternating current (AC) exciter during an asynchronous starting mode to generate a rotating field in the exciter, and consequently, to generate torque. The torque rotates the common rotatable shaft until the synchronous exciter can produce sufficient AC voltage at the output of the exciter rotor winding to power the main rotor, allowing synchronous running mode.